Field of the Disclosure
The present disclosure relates to a machine tool and a workpiece machining method, which are able to effectively suppress chatter vibration in machining a workpiece.
Background of the Disclosure
It has been well known that, when a workpiece is machined using a machine tool, chatter vibration deteriorates machining accuracy (in particular, surface accuracy). Such chatter vibration is roughly classified into forced chatter vibration and self-excited chatter vibration, and it is considered that forced chatter vibration is caused by an action of an excessively large external force or by synchronization between a frequency of an external force and a resonance frequency of a vibrating system and, on the other hand, self-excited chatter vibration is caused by continuation of cutting in which periodic variation in cutting resistance and periodic variation in thickness of cut enhance each other through interaction therebetween (the so-called “regeneration effect”).
Further, as a machining method in which self-excited chatter vibration is suppressed, there has been proposed a machining method in which the rotational speed of the spindle is varied in a periodic manner with a predetermined amplitude with the feed speed of the tool being fixed; such a machining method is disclosed in Japanese Unexamined Patent Application Publication Nos. S49-105277; 2000-126991; and 2012-091283. In each of the machining methods disclosed in the Japanese patent documents noted above, the rotational speed of the spindle is varied with predetermined amplitude and period in order to break periodicities of variation in cutting resistance and variation in thickness of cut, and, as a manner for varying the rotational speed of the spindle in a periodic manner, there has been proposed such a manner that the rotational speed of the spindle is varied in the form of a triangular wave or in the form of a sinusoidal wave.